Tendon healing in a bone tunnel differs at the tunnel entrance versus the tunnel exit: An effect of graft-tunnel motion?

Background: Motion between a tendon graft and bone tunnel may impair graft incorporation and lead to tunnel widening. Hypothesis: Healing of a tendon graft in a bone tunnel is inhibited by graft-tunnel motion. Study Design: Controlled laboratory study. Methods: Anterior cruciate ligament reconstruction was performed in 5 cadaveric rabbit limbs, and 3-dimensional graft-tunnel motion was measured using micro-computed tomography. The authors then performed bilateral anterior cruciate ligament reconstruction in 15 rabbits and used histomorphometry to compare tendon-to-bone healing between the tunnel aperture, midtunnel, and tunnel exit and between the anterior and posterior aspects of the tunnel. Results: Graft-tunnel motion was greatest at the tunnel apertures and least at the tunnel exit in cadaveric testing. Healing of the graft was slowest at the tunnel apertures. Tendon-bone interface width was greater at the aperture than at the tunnel exit for the femoral tunnel (P = .04). There was an inverse correlation between time zero graft-tunnel motion and healing in the femoral tunnel (P = .005). There was closer apposition of new bone to the tendon graft in the posterior half of the interface (P < .05). Osteoclasts were found at the tunnel apertures. Conclusion: Although graft-tunnel motion was only measured in cadaveric animals, results suggest that healing may be affected by the local mechanical environment, as graft healing in the femoral tunnel was inversely proportional to the magnitude of graft-tunnel motion. Clinical Relevance: Graft-tunnel motion may impair early graft incorporation and may lead to osteoclast-mediated bone resorption, contributing to tunnel widening. Early, aggressive postoperative rehabilitation may have detrimental effects on graft-to-bone healing.